This invention relates to band saw machine which includes a workpiece table for supporting a workpiece advanced thereon in a feed direction; a saw band for severing the workpiece in a cutting plane on the workpiece table in consecutive sawing steps; a saw band support for swinging the saw band out of the cutting plane after each sawing step, for swinging the saw band into the cutting plane before each sawing step and for maintaining the saw band in the cutting plane during each sawing step; openable and closable cooperating clamping jaws disposed downstream of the cutting plane as viewed in the feed direction for clamping the workpiece undergoing sawing the saw band; and openable and closable cooperating feed jaws for advancing the workpiece toward the cutting plane in the feed direction. The feed jaws which are disposed upstream of the cutting plane, are, in sequence, openable after closing the clamping jaws and before termination of a cutting step, shiftable away from the cutting plane to an extent of a successive work piece feed and closable on the workpiece for moving the workpiece against the feed direction away from the cutting plane after the sawing step.
Examples of band saw machines of the aforementioned type include both so-called horizontal band saws, including those having a pivotable upper part, and so-called vertical band saws. These saws serve in sectioning a metallic workpiece material that is typically present in the form of individual metal rods or bundles of metal rods, but can also be in another form that is suitable for processing on such band saw machines.
The workpiece material is conveyed to the cutting region of the band saw machine, in which it lies on a workpiece table, by way of a conveyor track disposed upstream of the workpiece table. The separated sections are cleared on the side of the cutting plane opposite the conveyor track by advancing the previously separated section, with the advance of the workpiece material, by the amount of the section to be separated next.
In band saw machines of the discussed type, the workpiece material is held for the cutting cycle by a pair of clamping jaws that open and close transversely to the direction of material feed, but are immovable in the direction of material feed; the jaws can be disposed behind the cutting plane, in relation to the feed direction of the workpiece material. The material feed is effected by a pair of opening and closing clamping jaws which are disposed on the supply side of the material and which are displaceable in the direction of material feed.
As mentioned at the outset, in the described metal band saw machines, the saw band circulating endlessly over two running wheels is guided by saw-band guides in the cutting region next to the workpiece material, and pivoted into the cutting plane, which extends in a different direction from the circulation plane of the saw band, to assure an endless supply and removal of the workpiece material. The saw-band guides, which are advisably positioned as close as possible next to the workpiece material, generally have hard-metal sliding parts on both side of the saw band and, perpendicular to these parts, hard-metal sliding parts or running rollers against the rear of the saw band. One of the two lateral band guides is usually fixedly mounted to the associated guide arm, while the opposite band guide is either set at a fixed distance with respect to the first lateral band guide, or is pressed against the saw band by means of a spring force or a hydraulic force for guiding the saw band with as little play as possible between the two lateral band guides.
When a cutting cycle is complete, the cutting run of the saw band must be moved backward through the cutting gap again to effect the return stroke. This causes the lateral cutting edges of the saw band teeth to slide along the workpiece material; at high band speeds, the teeth are subjected to considerable wear. Moreover, when material bundles are cut, the danger always exists that the rear of the saw band will be caught on a piece of material that protrudes slightly or changes its position. Therefore, the guide arms are often equipped with sensing elements that detect the sliding of the saw band out of the band guides for avoiding severe damage to the saw band.
To remedy the above-described problems, it is already known to space the workpiece material from the cutting plane, or to move it away from the cutting plane on the supply side thereof, after the cutting cycle has ended. The material is spaced by the clamping jaws that are movable in the direction of material feed.
The spacing of the material on the supply side of the cutting plane permits the cutting run of the saw band to be free from workpiece material on at least one side during the saw-band return stroke, so it can evade edges that may be protruding, thereby reducing the wear of the side edges of the saw-band teeth. In connection with hard-metal blades, which are frequently soldered to the teeth of the saw band in contemporary machines, however, this measure is no longer sufficient. Rather, a contactless return stroke of the saw band is becoming increasingly significant.
A contactless saw-band return stroke could be attained through the spacing of the workpiece material from both sides of the cutting plane following the cutting cycle. This, however, would mean that the clamping jaw pair which is immovable in the feed direction of the workpiece material and which is disposed behind the cutting plane, would have to be adjustable in the material-feed direction, which would require a considerable structural outlay and more space.
It is therefore an object of the invention to improve the apparatus of the type mentioned at the outset such that, following the cutting cycle, the return movement of the saw band is effected in a simple, space-saving and cost-effective manner, free from any contact with the workpiece material.
Regarding the apparatus mentioned at the outset, the object is accomplished according to the invention in that, for the return stroke of the saw band, the saw band support can be shifted away from the cutting plane, perpendicularly to the cutting plane, and in the direction of the spaced workpiece material. The effect of these measures is that, starting from a one-sided spacing of the workpiece material from the cutting plane, as is the case following the cutting cycle, the saw band is freed from the workpiece material on both sides because it is adjusted in the direction of the material spacing. Of course, in all of the embodiments of the invention, the magnitude of the adjustment of the cutting run of the saw band is dimensioned smaller than the control variable for the spacing of the workpiece material from the cutting plane. The saw band can, however, be adjusted without additional space requirements and with comparatively simple means. It is apparent that only a slight, simple adjustment to the saw-band guides is required to attain the effect sought with the invention. The adjustment of one of the two saw-band guides is basically sufficient, because the associated inclined position of the saw band suffices to free the band from the workpiece material. Of course, both guides can also be adjustable to keep the magnitude of the setting movement of the individual guides small. This measure of the invention does not necessitate additional space, because the saw-band guides are completely free in the relevant direction anyway.
According to a first solution involving an apparatus in which the saw band moves between hard-metal sliding parts inside the guides, it is provided in accordance with the invention that the hard-metal sliding parts are disposed at a respective end of setting means seated in the guides, and the setting means can be adjusted equidistantly between stops. Hydraulically- or pneumatically-actuatable cylinder-piston assemblies can be provided as setting means. In this way, the sliding guides for the saw band are merely shifted away from the cutting plane by a small amountxe2x80x940.5 mm to 1.0 mm sufficexe2x80x94prior to the return-stroke motion of the saw band; to this end, the cylinder-piston assemblies are correspondingly actuated with the aid of the automatic control of the band saw machine. After the return stroke of the saw band has been completed, the cylinder-piston assemblies are actuated in the reverse order for guiding the saw band in the cutting plane for the next cutting cycle.
According to a different design, in which at least one of the guides is adjustable, together with the guide arm supporting it, in essentially the direction of motion of the cutting run of the saw band on a guide track of the stand of the band saw machine, in the solution offered by the invention, the adjustable guide arm can be acted upon by a force acting in the direction of the spaced workpiece material, and the guide arm can be pivoted by this force for the return stroke of the saw band. A conceivable modification of this concept involves the continuous action of the force on the guide arm, and the option of increasing the guide play of the guide arm for the return stroke of the saw band.
The effect of these measures is that, due to the increase in the guide play of the movable guide arm, the guide arm has a certain freedom of motion with respect to its guide track, and is tipped somewhat within the guide track due to the effect of the aforementioned force, resulting in the adjustment of the saw band guide, and thus of the saw band, according to the invention. Of course, the means for changing the guide play can be turned on and off automatically by the process control of the band saw machine such that the guide arm is connected to its guide track with as little play as possible for the respective cutting cycle, and the guide play is increased for the return stroke of the saw band.
If, in the design described above, the workpiece material is held next to the cutting plane during the cutting process by a pair of clamping jaws that open and close parallel to the cutting plane through the movement of at least one of the clamping jaws, but are immovable in the direction perpendicular to the cutting plane, and the movable clamping jaw and the adjustable guide arm are associated with one another, it can be provided that the movable clamping jaw at least indirectly forms the abutment for the force acting on the guide arm. The background for this is that the movable clamping jaw and the adjustable guide arm are coupled to one another here for adjusting the mutual spacing of the two band-guide arms to the cross section of the workpiece material to be processed, the cross section being reflected equally in the work position of the movable clamping jaw.
The force acting on the adjustable guide arm can be a spring force that is preferably effected by a compression spring.